Starting around 9:15 a.m. ET, a number of Office 365 customers began reporting on Twitter that they were unable to sign into that service because of an MFA issue. Office 365 is one of a number of Microsoft services that uses Azure Active Directory MFA to authenticate.

“Impacted customers may experience failures when attempting to authenticate into Azure resources where MFA is required by policy. Engineers are investigating the issue and the next update will be provided in 60 minutes or as events warrant,” the dashboard status said.

Update (11:40 a.m. ET): The mitigation has begun. From the Azure status page:

“CURRENT MITIGATION: Engineers are currently in the process of cycling backend services responsible for processing MFA requests. This mitigation step is being rolled out region by region with a number of regions already completed. Engineers are reassessing impact after each region completes.”